Method for the explosive section forming of vessels



Oct. 3, 1967 v KUNSAGI ETAL METHOD FOR THE EXPLOSIVE SECTION FORMING OF VESSELS Filed June 25, 1965 s Sheets-Sheet 2 INVENTORS 4,452.40 AU/VSAG/ WILL/AN 1?. APBL'TzJ/Z. 5. MARK JORGE/v55 WWW m4 ATTORNEY Oct. 3, 1967 KUNSAGI ETAL 3,344,509

' METHOD"FOR THE EXPLOSIVE SECTION FORMING OF VESSELS v I Filed June 25, 1965 5 Sheets-Sheet 3 045240 Kl/IVSAG/ Y W/L MAN 1?. APBLETZJE. @6 .5. MARK TOPGFE/VSEN ATTORNEY Oct. 3, 1967 KUNSAGI ETAL 3,344,509

METHOD FOR THE EXP LOSIV E SECTION FORMING VESSELS Filed June 25, 1965 5 Sheets*Shee-t 4 INVENTORS Oct. 3, 1967 KUNSAGI ETAL 3,344,509

METHOD FOR THE EXPLOSIVE SECTION FORMING OF .VESSELS Fil ed June 25, 1965 r 5 Sheets-Sheet 5 v I %5' 4 \W 2 I 324 INVENTORS 45240 KUAAF/IG/ W/AL/AN le- APBLE'TZIIE, 5. MARK J'ORGE/VSEN ATTORNEY United States Patent 3,344,509 METHOD FOR THE EXPLOSIVE SECTION FORMING 0F VESSELS Laszlo Kunsagi, New York, N.Y., and Svend Mark Jorgensen, Tenaily, and William R. Apblett, Jr., Metuchen, N.J., assignors to Foster Wheeler Corporation, New

York, N.Y.', a corporation of New York Filed June 25, 1965, Ser. No. 467,040 Claims. (Cl. 29-421) This invention relates to the manufacture of pressure vessels. In particular, it relates to the manufacture of long vessels by explosive expansion of short length sections.

The present manufacture of pressure vessels and long rocket casings is accomplished through techniques which are expensive and require careful operational control.

Large rocket casings have been made by rolling and welding which is then followed by a costly jigging operation to achieve dimensional control. Heat treating is next applied for obtaining high strength metal characteristics. These operations entail considerable expense and add to the complexity of manufacture.

For small rocket casings shear spinning and drawing techniques are commonly utilized. These techniques are expensive and require heat treating of the casing for strength. Furthermore, exotic and costly casing metals are often utilized to achieve high strength casing design, thereby imposing additional expense,

As a result of heavy fabricating equipment, the manufacture of rocket casings is frequently performed at plants located far from the rocket launch site where the manufacturing jigs and equipment are located. This presents transportation problems in moving large rocket casings from the plant of manufacture to the launch site.

Furthermore, rocket casings are often made in short cylindrical sections which are then welded together circumferentially. Alignment of the cylinders before welding requires expensive jigs. Defects in the welds are not uncommon, especially where exotic materials are required and Welding techniques have not yet been perfected.

Accordingly, the present invention provides for the economical manufacture of casings from relatively short, rolled and Welded cylindrical, but otherwise unformed steel sections. First, an explosive forming operation is performed without a die. By this operation, the section is expanded close to a predeterimned final size. The expanded section is then sized with an explosive sizing operation into a light walled sizing die of substantially the same length as the section, the interior of which is machined to the dimensional tolerance of the desired final casing size.

The initial explosive forming operation is performed by utilization of a balanced charge, i.e., a preselected charge which produces a predetermined limited expansion without any die. This operation may be performed either within or without the sizing die. Where the initial explosive forming operation is performed within the die, the explosion expands the section to within a few percent of the sizing die, the die having no substantial effect on the expansion.

The present invention uses a light walled sizing die for the sizing operation. When a die serves the purpose of sizing only a substantially lighter die design may be used than an explosive forming die of standard design which serves primarily to limit the expansion.

Ultrahigh strength martensitic steel may be developed from sections made of austenitic stainless steel during the initial forming operation. A suflicient transformation from austenitic to martensitic steel may be achieved by properly selecting the austenitic composition, percent of expansion, temperature conditions and explosive conditions.

T 0 increase the length of the casing, an expanded section is joined in tandem to an unformed second section. The

3,3445% Patented Oct. 3, 1967 second section is explosively formed as the first by the explosive forming and sizing operations. Other sections are then added and the operations are repeated until a rocket casing of desired length is fabricated.

The sections may be joined by welding or by a corrugated jointure. Where section to section welding is performed, the section portions adjacent the ends to be welded are welded while in the austenitic state. This state is known to have good weldability properties. Subsequent expansion of the Weld and the proximate vicinity results in a homogenous ultrahigh strength crystal structure of the entire weld and surrounding area.

Where the sections are joined by a corrugated jointure, the sections portions adjacent the ends to be joined are circumferentially corrugated into overlapping mating and locking engagement.

With the above methods and apparatus, considerable ease of manufacture and savings in costs and labor are achieved. Excellent rocket casing design is accomplished. Fabrication may conveniently be made at the rocket site. The manufacturing die is light. Exotic materials are made unnecessary. High strength casings and jointures are readily developed. Further heat treatment is not required to strengthen the casings.

These and other advantages will appear more fully from the detailed description of a preferred method and embodiment in accordance with the accompanying drawings of which:

FIGURE 1 is a plan section taken on line 1-1 of FIG. 2 of the pressure vessel head prior to primary expansion of the heads;

FIGURE 2 is a vertical section of the tank head of FIG. 1 prior to primary expansion, and, in dot and dash lines, after primary expansion;

FIGURE 3 is a vertical section of a tank head placed in the sizing apparatus;

FIGURE 4 is a vertical section showing the sized head and the first cylindrical section aligned by an expandable hydraulic positioner;

FIGURE 5 is a plan section taken on line 55 of FIG. 4;

FIGURE 6 is an enlarged vertical section of the cylinder strength hardening and sizing apparatus;

FIGURE 7 is a vertical section showing the apparatus for welding the second head to the casing;

FIGURE 8 is a vertical section showing the strength hardening expansion apparatus and the sizing apparatus for the second head and the reverse curve portion of the final expanded cylindrical casing section;

FIGURE 9 is a broken elevation view of a completed rocket casing;

FIGURE 10 is an enlarged vertical section of the expanding and sizing apparatus for corrugated joining; and

FIGURE 11 is a broken elevational view of a corrugated joined rocket casing manufactured by the apparatus of FIG. 10.

Reference is now made to FIGS. 1 and 2 for a method of forming hemispherical rocket casing heads. A primary head unit 11 from which the final rocket casing head is made is a closed vessel made of A151 301 austenitic stainless steel consisting of a short cylindrical portion 12, four conical frustums 13, two at each end of the cylindrical portion, and two circular flat sections 14 welded together along edges 9. The frustums are differently shaped so that the unit approximates two hemispheres joined by a cylinder. A number of short spacer bars 19 are Welded to the cylindrical portion 12 midway between its ends to hold it in position between two circular split rings 15, split at point 26 in its circumference. The split rings 15 engage substantially the entire circumference of the cylindrical portion 12 to prevent the cylindrical portion from being expanded upon explosion. The assem- 3 bly is mounted on a ring support 20 supporting the bottom-most split ring 15.

At ambient temperature, the split rings 15 are not completely closed at point 26 providing a small gap in the circumference of the ring. The primary head unit 11 is filled to the top with liquid nitrogen 16 through the bottom connection 28 lowering the temperature of the head unit to 320 F. and a balanced explosive charge 17 is inserted into the head unit and suspended from top connection 29. As the head unit 11 contracts at lower temperatures, the gap at point 26 (shown closed in FIG. 1) is closed by tightening the bolts 41 of C-clamps 27, thereby tightening the rings against the circumference of the cylindrical portion.

Charge 17 is then detonated by detonation equipment 31 and explosively expands the head unit as shown by the dot and dash lines 18 in FIG. 2, forming joined expanded hemispherical heads 18a and 18a. The size and configuration of balanced charge 17 is selected so that it is sufiicient to expand the heads close to the required spherical shape.

The cylindrical portion 12 does not expand as a result of the inhibiting effect of rings 15, except where the remote edges 15a of the rings are rounded, permitting a slight expansion of the top and bottom edges of cylindrical portion 12. In the expansion, reverse curves are formed joining the cylindrical portion 12 with the upper and lower expanded hemispherical heads 18a and 18a. For the purposes of this application, reverse curves and the cylindrical portion 12 shall be defined as constituting upper and lower bracketed reverse curve transition sections 33.

In this particular embodiment the balanced charge is chosen so that the expansion is approximately 18% to 22% at --320 F. (the temperature of liquid nitrogen). As a result, the expanded head unit 18 acquires ultrahigh strength by a transformation of the austenitic stainless steel material to martensite at the portions of expansion. Reverse curve transition sections 33 do not fully trans form nor do cylindrical portions 12 for at these temperatures, the transformation for many ordinary grades of AISI 301 austenitic stainless steel goes nearly to completion for expansions of at least 18% to 22%. At other temperatures, and other austenite steel compositions, different expansion will produce the ultrahigh strength characteristics.

The austenitic stainless steels, particularly AISI 301, are noted for their work hardening capabilities. In A151 301 stainless steels, the composition is or can be balanced so that the austenitic structure is highly unstable at subzero temperatures and that a comparatively small amount of deformation will result in the transformation of the metastable austenite into high strength martensite.

Stainless steels, in which the properties have been enhanced by the effects of such cold work, are attractive for rocket case applications because their properties include high strength coupled with good corrosion resistance and relatively good toughness characteristics.

Prior to the straining, the austenitic material is relatively weak and ductile and has excellent formability and weldability characteristics. Forming and welding the cylindrical portion 12, conical frustums 13, and flat sections 14 is conducted prior to the strength hardening expansion operation. Heat treatment of the completed case is not required although the properties of the material may be further enhanced by martensitic strain hardening or by a relatively low temperature aging treatment, if so desired.

After expansion, the pressure in the expanded head unit 18 is released and the remaining liquid nitrogen is drained back to storage through bottom connectors 28. As the temperature of the unit returns to ambient temperature, the C-clamp bolts 41 are loosened .When the whole assembly is at ambient temperature, the bolts 41 are retightened. The expanded head unit 18 is then removed from ring support 20 and is sectioned into two halves by cutting the cylindrical portion 12 in the middle thereof between the split-rings 15.

Upper head 18a (one of the halves of expanded head unit 18) with its retaining split ring 15 is placed in a sizing die 21 as shown in FIG. 3 which has a support 22. The sizing die 21 comprises a heavy hemisphere machined on the inside surface 23 with close dimensional tolerances to predetermined dimensions conforming to the desired final shape of the heads. Retaining ring 15 engaging the top edge of head 18a, rests on the upper edge of sizing die 21, supporting the head within the die so that the inside surface 23 of the die 21 and the outer surface 24 of the head define a small clearance 25 therebetween. The initial expansion was chosen to be close to the dimensions of the sizing die so that the sizing die may be relatively thin walled since it is solely used for the sizing operation.

The head 18a is then filled to a predetermined level 45 with a liquid transmitting medium 44 such as water. Explosive charge 46 is placed on support 47 within medium 44 and is then detonated. The detonation expands head 18a into contacting proximity with the inner surface 23 of the die.

After detonation, split ring 15 is removed from the sized head and the free circular edge 48 of the head is machined for welding. An opening 51 (FIG. 4) is cut in the top of the head, and the edge 52 formed by the hole is machined. A lifting rig 55 for attachment to a hoist is fitted inside the opening 51. Head 18a is then lifted to permit installation of an expander ring 56 (also shown in FIG. 5) inside the head.

As may be seen in FIG. 4, head 18a is then placed on top of a first cylinder section 57 of same diameter as that of cylindrical portion 12, having a free upper edge 50. The expander ring 56 is fitted inside the adjoining edges 50 and 48 which are to be welded, and is activated by a hydraulic cylinder 58. When pressure is admitted into the hydraulic cylinder 58, the expansion of expander ring 56 aligns the contiguous edges 48 and 50 and eliminates small diametrical differences. Welding of the aligned edges is then accomplished by a circumferential welding machine 59, after which the expander ring 56 and hydraulic cylinder 58 are hoisted up by cables 61 and secured to the top of the head as shown in FIG. 6.

Reference is now directed to FIG. 6 whereby the cylinder section 57 is first explosively strength hardened to obtain ultra-high strength and secondly explosively sized.

An upright cylindrical core 63 made of aluminum concentric to a light die is disposed on a liquid tight base. The die 85 is equal in length to the length of a section 57 plus the length of a reverse curve transition section 33. In this example, the inner die wall 84 of die 85 is selected to be approximately 25% larger than the diameter of the cylinder section 57.

An annular balanced cylindrical charge 65 is mounted on a suitable liner 64 made of a material such as flexible board, plastic, aluminum or tinplate, either ferrous or nonferrous.

The quantity of explosive in the balanced charge varies along portions of the length of the liner 64, but is equally distributed in all radial directions from the axis at every portion along the length perpendicular to its axis in such a manner so that upon detonation the resultant explosion causes cylinder 57 to expand close to the desired final shape. The balanced charge for this and the expansion of FIG. 2 is selected by the method described in copending patent application Explosive Forming With Balanced Charges, Ser. No. 339,551, filed on Jan. 22, 1964, which is 20w US. Patent 3,235,955 having issued on Feb. 23, 19 6.

In this example, the balanced charge is selected to expand cylinder 57 into shape 82 within a few percent of the die 85 indicated by dot and dash lines in FIG. 6.

Once the balanced charge 65 is determined and mounted on liner 64 (this step is performed outside of the die 85 and core 63), it is covered by insulation layer 71 and a water-proof covering 72 to form charge assembly 70. The charge assembly is then installed about and concentric with the core 63 as shown in FIG. 6. The charge liner 64 may be packed around the base or it may be placed in a shallow groove 66 which is filled with water frozen by admitting a small amount of liquid nitrogen into the area of the groove.

A temporary shield 60 is placed around the charge assembly and water is pumped into the space 67 between core 63 and liner 64. At the same time, liquid nitrogen is admitted via conduit 68 to the space 88 between the temporary shield 60 and the covering 72 to freeze the water inside the space 67. After a solid layer of ice has been formed in 67, the temporary shield 60 is removed.

The rocket case end assembly designated 62 consisting of head 18a and cylinder section 57 circumferentially welded together is then hoisted up and placed Within die 85, concentric to the die 85 and to both core 63 and charge liner 64. The assembly 62 is fitted inside an annular upside down U-shaped reverse curve forming ring 77 formed along the lower inside surface of external die 85, the ring 77 defining an inner toroidal gap 76 wth apertures 80 in communication therewith. A washer-like closure plate 74 is installed at the top of the core 63 reaching from the core to the rocket case end assembly 62 and a nitrogen pipe line 75 is installed between the closure. plate 74 and the gap 76.

Liquid nitrogen is admitted via conduit 68 to completely fill the whole space 69 up to closure plate 74 and between the rocket case section 57 and the covering 72 of charge assembly 70. During the initial stage of this operation, the liquid nitrogen will almost immediately flash into vapor, which will flow upward to the cover plate 74 and then downward through pipe line 75 through the reverse curve ring gap 76, out through apertures 80 in the ring, and upward outside the rocket case end assembly 62. Gradually, a stable temperature gradient Will be established, and the liquid nitrogen level will build up to a level near the top plate. The nitrogen pipe line 75 will be disconnected from closure plate 74 and swung toward the center of the core (not shown).

The balanced charge 65 is then detonated by detonating equipment (not shown) to cause a rapid shock wave to be transmitted through the liquid nitrogen transmitting medium within region 69 to impact the cylinder 57 and reverse curve transition section 33 welded thereto causing them to rapidly expand to the shape as indicated by dot and dash lines 82. Outer die 85 does not limit this expansion.

. The balanced charge contains varying quantities of explosive at the top portion of the charge 65 sufficient to expand reverse curve portion 33 of the rocket case end assembly 62 into the shape 82. In this example, the reverse curve forming ring 77 limits the expansion of the lower part of cylinder 57 to the shape of the ring. However, the balanced charge 65 could be selected and proportioned with varying explosive quantities so as to limit the expansion of cylinder 57 at the lower part without the reverse curve forming ring 77 i.e., without any die portion serving to limit the expansion of the cylinder 57 and still form the expanded shape defined by the dot and dash lines 82.

The balanced charge is selected so that the expansion at the circumferential weld between edges 50 and 48 (as Well as the adjacent portions and the cylinder 57) is approximately 18% to 22% at 32() F. As a result of this expansion, the expanded weld and adjacent portions acquire ultrahigh strength by a transformation of the austenite to martensite.

The remainder of the expanded end assembly, including the AISI 301 austenitic steel cylinder 57, undergoes a transformation to martensitic steel at the portions of expansion as does the weld since the expansion is also between 18% to 22%. However, little transformation oc curs at the lower portion of the end assembly adjacent 6 the reverse curve ring 77 where expansion does not occur.

The expanded end assembly 62 is then hoisted up to permit the site to be flushed free of debris and to permit installation of a cylindrical sizing charge assembly (not shown, but in the place of balanced charge assembly 70) concentric with and around core 63. A sizing operation is then performed with the aid of external die 85. This die is machined with close dimensional tolerances on the internal surface 84 to the desired predetermined final size of the end assembly. The die 85 is thin walled as the sizing expansion is small since the expanded end assembly is within a few percent of the inner diameter of the die. The die is merely used so that the end assembly achieves the required final dimensional tolerance.

As in the explosive strain hardening operation, a temporary shield is installed, water is pumped into the space between the sizing charge assembly and the core 63 and is frozen by liquid nitrogen entering the space between the temporary shield and the sizing charge assembly. The temporary shield is then removed and the expanded rocket case end assembly is lowered and fitted inside the die 85 and reverse curve forming ring 77 along the dot and dash lines 82. The annular space between the sizing charge assembly and the rocket case end assembly 62 is filled with water at ambient temperature, the water acting as the transmitting medium for the sizing operation. The sizing charge assembly is not fully balanced since the die 85 is used somewhat to limit the small expansion. However, a balanced charge may be readily utilized in place of the die without departing from the scope of the present invention. The sizing charge is then detonated to cause the expanded end assembly 62 to expand into the die wall 84, the desired predetermined final size.

After the sizing operation, the die 85 is opened and the expanded end assembly is hoisted up and placed on top of a second cylinder section identical to section 57 in the same manner as the head 18a Was placed on the first cylinder section 57. The two sections are then aligned as before by the hydraulic expander ring and welded together. The welding does not destroy the martensitic properties of the expanded casing since the welding is confined to the unstrained bottom portion of the rocket case end assembly which was limited in expansion by the reverse curve ring 77.

After welding, the added section, unstrained end of the expanded casing and weld are inserted into the die a before and the previously described strain hardening and sizing operations are performed. Additional unformed cylinder sections may be added, strain hardened, and sized in the same manner until a rocket casing of desired length is formed.

The die 85 is built up of two light cylinder sections, upper die section 86 and lower die section 87. Each section is split longitudinally into two half shells held together by C-clamps similar to those shown in FIGS. 1 t0 3 and bolted to one of the half shells.

Following the sizing expansion of a last cylinder section, the lower die section 87 is opened (releasing the above mentioned C-clamps) and the rocket casing is lifted out of the lower die section 87. The upper die section 86 is not opened and remains clamped to the last sized cylinder section as may be seen in FIG. 7. The casing assembly is placed on top of the other half of expanded head 18a which has been sized inside head sizing die 21.

The two dies, upper die section 86 and head sizing die 21, are kept separated by spacer bars 91. The expander ring 58 is positioned and head 18a and the casing assembly and head are welded together. Spacer bars 91 are then removed and die section 86 is opened so that it may be lowered to rest on the sizing die 21 as shown in FIG. 8. The head 18a is then filled with water up to the lowest reverse curve ring which is frozen into ice 104 by the addition of liquid nitrogen.

An inner core 92 small enough to fit through the opening 51 is prepared outside the rocket case assembly. It is filled with water 103 which is then frozen and a balanced annular charge 93 is attached to the outside of th core. The core is then inserted through the top opening of the rocket casing assembly and placed on the ice 104 inside the head 18a. The annular space around the core 92 is then filled with liquid nitrogen 102. Charge 93 is detonated and the two reverse curve transition sections and circumferential weld therebetween 33 expand close t the desired shape as indicated by dot and dash line 95. The circumferential Weld and the expanded portions adjacent thereto transform into ultrahigh strength martensitic steel.

The core 92 is then removed and a second core is put in its place supporting a suitable sizing charge. The expanded portions are sized into the die wall 84, as above, with the annular space around the core being filled with water at ambient temperature for the liquid transmitting medium.

FIG. 9 shows the completed rocket casing. Circumferential weld lines 96 merely indicate the demarcation between the added cylindrical sections 51. It should be noted that the strain hardening operation actually produces section Welds which are homogenous with the adjacent section portions. The broken lines indicate that any number of sections may be used to build any desired length casings.

Small scale fabrication was performed using the above method and die apparatus. The technique was to expand ordinary grade AISI 301 stainless steel cylinders between 8% to 25% strain into a die and then pressurize them to test their ultrahigh strength characteristics. The thickness of the cylinder sections 57 were of an inch; the outer diameter, before expansion, 6.25 inches.

Prior to expansion, the cylinders were rolled to the above dimensions and welded with an inert gas shielded tungsten arc process. The weld was made using a single flange butt joint preparation. Both ends of the cylinder being sealed, the inside was purged by argon gas during the welding of the outside seam, and afterwards the inner seam was welded with filler material cut from the parent material. The rolled and welded cylinders were carefully centered in the die, the bottom sealed with Ductseal and filled up with liquid nitrogen.

The first explosive strain hardening operation expanded the cylinder close to the dimensions of the die facilitating the transformation of the austenitic rystal structure into martensite. The sizing operation was performed at ambient temperature with water as the energy transmitting medium to size the cylinder by sealing it into the die. Since only a light charge is required for the sizing of this operation, the die was correspondingly light.

The explosive used was a Primacord line charge, care fully centered and initiated at the top. The size of th charge was established through experimentation and it was found that at liquid nitrogen cryogenic temperatures 500 gr./ft. was required for 24% expansion, 400 gr./ft. for 20%, 350 gr./ft. for 18% and 300 gr./ft. for a 13% expansion. The sizing charge was 200 gr./ft. which expanded the cylinders tightly into the die after the primary strength hardening expansion.

The chemical composition of the stainless steel and weld by percentage of weight was as follows:

Fe Remainder Prior to straining, the room temperature tensile strength was less than 100,000 p.s.i. One group of cylinders Was explosively strained at cryogenic temperature to 9.5% strain followed by further expansion to 12.8% strain at ambient temperature in the explosive sizing operation. In subsequent pressurizing tests at room temperature, these cylinders failed at 197,000 p.s.i. stress load after 10.2% further straining. In computing this stress, it was assumed that the load during pressurizing was uniaxial.

One cylinder was strained to 14.0% strain at cryogenic temperatures and to 17% strain in the sizing operation. It failed in pressurization in the weld at 233,000 p.s.i. stress level after 4.0% further straining.

A third specimen was strained to 18.2% strain at 320 F. and further to 20.3% strain in the sizing operation. In pressurizing, this specimen burst at 265,000 p.s.i. stress level after 6.3 further straining.

In another series of tests with another austenite composition, the outer diameters were 5.88 inches and 5.73 inches and they were expanded to 20% strain and to 24% strain, respectively. The cylinders were welded as before with the inert gas shielded tungsten process, but type 301 stainless steel filler wire was used.

The thickness of both the cylinders were of an inch and the chemical composition by percentage of weight was as follows:

Fe Remainder After the strain hardening expansion and sizing, the cylinders, which were strained to 24% strain, were tested. Two were pressurized and the first burst at 261,000 p.s.i. stress level after 8.2% further straining in pressurizing and the other burst at 268,000 p.s.i. after 7.7% straining.

The 5.88 inch cylinder was expanded to 20% strain and subjected to a low temperature heat treatment of 800 F. for 24 hours. It burst at 281,000 p.s.i. stress after 2.4% straining.

As a result of both series of tests, it was seen that due to the particular chemical composition of the various ordinary grade AISI 301 stainless steels, cryogenic expansions to between approximately 8% to 25 strain produce ultrahigh strength tensile strengths between 180,000 to 290,000 p.s.i. with corresponding yield strengths between 180,000 and 260,000 p.s.i. These tests also demonstate that for similar chemistries and conditions, the ultrahigh strength process is repeatably reliable.

Other tests were conducted With full scale cylinders with similar results.

Various other compositions of AISI 301 austenitic stainless steel may be utilized to produce the same ultrahigh strength characteristic as described above at other temperatures.

For example. the strength hardening operations may be performed at ambient temperatures where the rocket casing materials are balanced so as to be unstable at room temperatures. The following percentage composition by weight was non-explosively strained at room temperatures to approximately 20% to achieve 85% martensite transformation as reported by Southern Research Institute, in Development of High Strength and Fracture Toughness in Steels through Strain Induced Transformations Tech. Report No. WALTR 323.42-2 (May 10, 1963):

same as the equivalent straining of the above-mentioned ordinary AISI type 301 compositions under cryogenic conditions.

Other balanced compositions within the A181 type 301 range may be chosen experimentally to achieve high martensitic transformation by straining to other strain percentages (even beyond 8 to 25%) at various temperatures without departing from the scope of the present invention.

Reference is now made to FIGS. 10 and 11 for a method of joining the casing sections without welding by expanding two overlapping cylindrical sections into a light corrugated die 85'. The die 85' is again light walled as the primary strength hardening operation expands the vessel close to the final size. The die interior 97 is formed with identical circumferential corrugations 9-8 and 98' on the top and bottom portions of the die.

The cylindrical casing sections consisting of ordinary grade A181 301 stainless steel are formed, as before, by a two step explosive forming operation. First, a strain hardening operation is performed at cryogenic temperatures expanding the sections between 18% to 22% close to the die wall interior so as to achieve martensitic .portion of the expanded cylinder is placed into the mating upper die corrugations as shown in 98'. An unformed ,cylinder section 57 identical to the first is inserted into the die as shown and is explosively strain hardened and sized as the first cylinder. Upon strength hardening and sizing, cylinder section 57 is expanded into contiguous contact with the interior 97 of die 85' at all portions except the upper portion 98'. At the upper portion 98', cylinder 57 is corrugated into mating contact with the corrugated lower portion of cylinder 99 to form an air-tight high strength corrugated jointure (not shown). A duplicate jointure is -shown at 101 for two prior joined sections. In all other respects, the fabrication of the final corrugated rocket casing is the same as that described in conjunction with the fabrication of welded rocket casing.

Circumferentially shaped explosive charges may be used in the primary strain hardening operation to aid the corrugation formation without the aid of the die corrugations. The light walled die actually does not serve the conventional heavy die function since the first explosive step brings the cylinder within a few percent of the final shape.

As described before, the explosive forming operation causes the final corrugated jointure to be martensite hardened. The corrugated jointure so formed has the advantages of ease of inspection, simplicity of fabrication, ease I of alignment of cylinder sections, improved buckling and casing reinforcement, reduction of vibration problems,

and, speed in which the jointure can be made.

A complete rocket casing joined in sections by circumferential corrugations is shown in FIG. 11. In corrugation section manufacture, the head sizing equipment would also be provided with circumferential die corrugations so as to form corrugations.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. A method of manufacturing a metallic prising:

forming by means for explosively expanding a first vessel having an end portion with an opening therein vessel comwhile inhibiting expansion at said end portion to provide a neck in said end portion of said expanded vessel; connecting said explosively expanded first vessel to a second vessel which has an opening therein substantially of the same size and shape as the opening in said first vessel, said opening in said first vessel and said opening in said second vessel being aligned to produce a continuous connection between the opening of said first vessel and the opening of said second vessel; and explosively expanding at least a portion of said second vessel and the end portion of said said first vessel including the connection therebetween to enlarge the size of the second vessel and the end portion of the first vessel. 2. The method of manufacturing a vessel according to claim 1 wherein the explosively expanded first vessel is connected to the second vessel by welding.

3. The method of manufacturing a vessel according to claim 1 wherein the connection of the explosively expanded first vessel to the second vessel comprises:

disposing the explosively expanded first vessel and the second vessel in an overlapping relationship; and

corrugating the overlapping portions into a mating relationship coextensively with the explosive expansion of the connection. 4. A method of manufacturing a metallic vessel comprising:

forming a closed primary head unit including a central cylindrical portion, at least one conical frustum portion at each end of the cylinder, flat plate portions at the free ends of the frustums, the frustum portions having their narrowmost ends remote from the cylindrical portion to define an approximately oval configuration, the central cylindrical portion and the conical frustum portions and the flat plate portions being welded together; explosively expanding said primary head unit including welds into substantially two hemispherical portions while inhibiting expansion at the cylindrical portion so that the hemispheres are provided with a connecting neck of substantially the original diameter of the cylindrical portion at the cylindrical portion;

circumferentially cutting the expanded head unit in half along the center of the cylindrical portion to form two hemispherical vessels both with neck ends;

circumferentially connecting the neck end portion of one of said two hemispherical vessels to the end of a cylindrical vessel of substantially the same original diameter as said cylindrical portion; and

explosively expanding at least a portion of the cylindrical vessel and the necked down end portion of the hemispherical vessel connected thereto including the connection therebetween. 5. The method of manufacturing a vessel according to claim 4 wherein the hemispherical vessel is connected to the cylindrical vessel by welding.

6. The method of manufacturing a vessel according to claim 4 wherein the connection of the hemispherical vessel to the cylindrical vessel comprises:

disposing the hemispherical vessel and the cylindrical vessel in an overlapping relationship; and

circumferentially corrugating the overlapping portions into a mating relationship coextensively with the explosive expansion of the connection.

7. A method of manufacturing a metallic vessel comprising:

explosively expanding a first vessel having a circular cross-section and having an end portion with a circular opening therein while inhibiting expansion at said end portion so that said end portion necks down; connecting said explosively expanded first vessel to the end of a second vessel having a cylindrical shape and which has substantially the same diameter as said neck end portion; positioning at least a portion of the second vessel and the necked down portion of the first vessel including the connection therebetween within a cylindrical die, said cylindrical die having an interior die wall machined to predetermined dimensional tolerances;

explosively expanding the second vessel and the necked down end portion of the first vessel including the connection therebetween to within close proximity of the die wall; and

explosively expanding the second vessel and the necked down portion of the first vessel including the connection therebetween into engagement with the die wall. 8. The method of manufacturing a vessel according to claim 7 wherein the explosively expanded first vessel is connected to the second vessel by welding.

9. The method of manufacturing a vessel according to claim 7 wherein the connection of the explosively expanded first vessel to the second vessel comprises:

disposing the explosively expanded first vessel and the second vessel in an overlapping relationship; and

circumferentially corrugating the overlapping portions into a mating relationship coextensively with the explosive expansion of the connection.

10. A method of manufacturing a metallic vessel comprising:

forming a closed primary head unit including a central cylindrical portion, at least one conical frustum portion at each end of the cylinder, flat plate portions at the free ends of the frustums, the frustum portions having their narrowmost ends remote from the cylindrical portion to define an approximately oval configuration, the central cylindrical portion and the conical frustum portions and the fiat plate portions being welded together;

explosively expanding said primary head unit including its welds into substantially two hemispherical vessels while inhibiting expansion at the cylindrical portion so that the hemispherical vessels are provided with a connecting neck of substantially the original diameter of the cylindrical portion at the cylindrical portion;

circumferentially cutting the expanded head unit in half along the center of the cylindrical portion to form two hemispherical vessels both with neck end portions; circumferentially welding the neck end portion of one of said two hemispherical vessels to the end of a cylindrical vessel of substantially the same original diameter as said cylindrical portion to produce a continuous circumferential weld; positioning at least a portion of the cylindrical vessel and the neck end portion of the hemispherical vessel including the weld therebetween within a cylindrical die, said cylindrical die having an interior die wall machined to predetermined dimensional tolerances;

explosively expanding the cylindrical vessel and the neck end portion of the first vessel including the weld therebetween to within close proximity of the die wall; and

explosively expanding the cylindrical vessel and the neck end portion of the first vessel including the weld therebetween into engagement with the die wall.

11. The method of manufacturing a metallic vessel according to claim 10 wherein the vessels are made of austenitic stainless steel and the vessel composition, percentage of expansion of the cylindrical vessel and the neck end portion of the hemispherical vessel including the weld therebetween during the first expansion to within close proximity of the die wall, temperature and explosive conditions being preselected so that the austenitic steel undergoes substantial transformation to martensitic steel.

12. A method of manufacturing a metallic vessel comprising:

forming by means including explosive forming a first vessel having an end portion with an opening therein while inhibiting expansion at said end portion to provide a neck in said expanded vessel, said first vessel being initially austenitic stainless steel, said explosive forming taking place in two steps, the first step being carried out at cryogenic temperatures whereby the austenitic stainless steel is transformed to martensitic steel except at the neck end portion and the second step being carried out at ambient temperatures to size the vessel;

welding the neck end portion of said first vessel to the end of a second vessel of austenitic stainless steel, said second vessel having a cross-sectional size and hape substantially the same as said neck end portion of said first vessel;

positioning at least a portion of the second vessel and the neck portion of the first vessel including the weld therebetween within a die;

explosively expanding at least a portion of the second vessel and the neck portion of the first vessel including the weld therebetween at cryogenic temperatures to a position just slightly within the die wall; and

explosively expanding at ambient temperatures the portion of the second vessel already expanded and the neck portion of the first vessel already expanded into engagement with the die wall.

13. A method of manufacturing a metallic vessel comprising:

forming a closed primary head unit comprising a cylindrical portion, at least one conical frustum portion at each end of the cylinder, fiat plate portions at the free ends of the frustums, the frustum portions having their narrowmost end remote from the cylindrical portion to define an approximately oval configuration, the primary head unit being formed from austenitic stainless steel and welded together;

filling the primary head with a liquid nitrogen transmitting medium;

supporting a first balanced charge in the center of the primary head unit;

explosively expanding the primary head unit at the conical portions, flat plates, and welds therebetween at liquid nitrogen temperature by detonating the first balanced charge to increase the size of the head unit while inhibiting expansion at the cylindrical portion so as to retain substantially the original diameter at the cylindrical portion;

removing the liquid nitrogen transmitting medium;

circumferentially cutting the expanded head unit in half along the center of the inhibited cylindrical portion to obtain disjoined first and second expanded hemispherical heads with neck ends;

supporting the first expanded hemispherical head within a light hemispherical die having a die wall machined to predetermined dimensional tolerances, said die wall being slightly larger than said first expanded head defining a small clearance between the first expanded head and the die wall;

filling said first expanded hemispherical head with a water transmitting medium;

centrally supporting a second charge within the first expanded hemispherical head;

explosively expanding the first expanded hemispherical head into engagement with the die wall by detonating the second charge;

circumferentially welding the neck end portion of the first expanded hemispherical head to an end of a first cylindrical vessel of substantially the same composition and original diameter as said cylindrical portion;

positioning the first cylindrical vessel and the neck end portion axially within a cylindrical die having an interior die Wall, larger than the first cylindrical vessel and a length substantially equal to the length of the first cylindrical vessel plus the neck end portion;

selecting a third balanced cylindrical surface charge having a length substantially equal to the length of the first cylindrical vessel plus the length of the neck end portion and having a diameter smaller than the first cylindrical vessel;

disposing said third balanced cylindrical surface charge axially Within the first cylindrical vessel so that the third charge is adjacent substantially the entire first cylindrical vessel and the neck end portion including the weld therebetween;

filling the annular region around the third balanced charge with a liquid nitrogen transmitting medium;

expanding the first cylindrical vessel and the neck end portion of the hemispherical vessel by detonating the third charge to within close proximity of the interior die well while inhibiting expansion at the other end of the first cylindrical vessel opposite from the end welded to the neck end portion of the hemispherical vessel so that said other end remains substantially the original diameter of the vessel, the third balanced charge being selected to be sufficient to produce such expansion;

removing the liquid nitrogen transmitting medium;

disposing a fourth cylindrical surface charge in substantially the same position as the third cylindrical surface charge;

filling the annular region about the fourth cylindrical surface charge with a water transmitting medium; and

expanding the first cylindrical vessel and the neck end portion of the hemispherical vessel including the weld therebetween into engagement with the interior die Wall by detonating the fourth charge while still inhibiting expansion at the other end of the first cylindrical vessel, said fourth charge being selected to be sufficient to produce such expansion.

14. The method of manufacturing a metallic vessel according to claim 13 which further includes:

circumferentially Welding the neck end portion of the first cylindrical vessel to an end of a second cylindrical vessel of substantially the same composition and original diameter as the first cylindrical vessel;

positioning the second cylindrical vessel and the neck end portion of the first cylindrical vessel including the weld therebetween within the cylindrical die;

disposing a fifth balanced charge substantially identical to the third balanced charge axially within the second cylindrical vessel and adjacent substantially the entire second cylindrical vessel and the neck end of the first cylindrical vessel including the weld therebetween;

filling the annular region about the fifth charge with a liquid nitrogen transmitting medium;

expanding the second cylindrical vessel and the neck end of the first cylindrical vessel by detonating the fifth charge to within close proximity of the interior die wall while inhibiting expansion at the other end of the second cylindrical vessel opposite from the end welded to the first cylindrical vessel so that the other end remains substantially the original diameter of the vessel;

removing the liquid nitrogen transmitting medium;

disposing a sixth cylindrical charge substantially identical to the fourth charge but located in substantially the same position as the fifth charge;

filling the annular region about the sixth charge with a water transmitting medium; and

expanding the second cylindrical vessel and the neck end portion of the first cylindrical vessel including the weld therebetween into engagement with the interior die wall by detonating the sixth balanced charge while still inhibiting expansion at the other end of the second cylindrical vessel.

15. The method of manufacturing a metallic vessel according to claim 14 which further includes:

welding the neck end portion of the second cylindrical vessel to the neck end portion of the second hemispherical head;

filling the second hemispherical head with a water transmitting medium;

filling with liquid nitrogen the region formed by the neck end portion of the second cylindrical vessel and the neck end portion of the second hemispherical vessel and the weld therebetween;

disposing a seventh balanced cylindrical surface charge axially within and adjacent the neck end portion of the second cylindrical vessel and the neck end portion of the second hemispherical vessel including the weld therebetween;

expanding the neck end portion of the second cylindrical vessel and the neck end portion of the second hemispherical head including the Weld therebetween by detonating the seventh balanced cylindrical surface charge to Within close proximity of the ex panded diameter of the first cylindrical vessel and first hemispherical vessel, the seventh balanced charge being selected to be suflicient to produce such expansion;

filling the region within the expanded neck end portion of the second cylindrical vessel and the expanded neck portion of the second hemispherical portion including the weld therebetween with Water at ambient temperatures;

disposing the cylindrical die concentrically adjacent the expanded neck end portion of the second cylindrical vessel and the expanded neck portion of the second hemispherical portion including the weld therebetween;

disposing an eighth cylindrical surface charge axially within the expanded neck end portion of the second cylindrical vessel and the expanded neck portion of the second hemispherical portion including the Weld therebetWeen; and

expanding the expanded neck end portion of the second cylindrical vessel and the expanded neck portion of the second hemispherical portion including the weld therebetween into engagement with the interior die wall by detonating the eighth cylindrical surface charge, the eighth cylindrical surface charge being selected to be sufficient to produce such expansion.

References Cited UNITED STATES PATENTS 2,214,226 9/1940 English 166l 2,367,206 1/1945 Davis 29--421 2,779,279 1/195'7 Maiwurm 29-523 X 3,036,373 5/1962 Drexelius 29-421 3,037,374 5/1962 Williams 29470.1 X 3,140,537 7/1964 Popolf 29-474.3 3,160,949 12/1964 Bussey et a1. 29-421 3,197,851 8/1965 Aleck 29421 FOREIGN PATENTS 657,727 9/1951 Great Britain. 766,741 1/1957 Great Britain.

0 CHARLIE T. MOON, Primary Examiner.

THOMAS H. EAGER, Examiner. 

1. A METHOD OF MANUFACTURING A METALLIC VESSEL COMPRISING: FORMING BY MEANS FOR EXPLOSIVELY EXPANDING A FIRST VESSEL HAVING AN END PORTION WITH AN OPENING THEREIN WHILE INHIBITING EXPANSION AT SAID END PORTION TO PROVIDE A NECK IN SAID END PORTION OF SAID EXPANDED VESSEL; CONNECTING SAID EXPLOSIVELY EXPANDED FIRST VESSEL TO A SECOND VESSEL WHICH HAS AN OPENING THEREIN SUBSTANTIALLY OF THE SAME SIZE AND SHAPE AS THE OPENING IN SAID FIRST VESSEL, SAID OPENING IN SAID FIRST VESSEL AND SAID OPENING IN SAID SECOND VESSEL BEING ALIGNED TO PRODUCE A CONTINUOUS CONNECTION BETWEEN THE OPENING OF SAID FIRST VESSEL AND THE OPENING OF SAID SECOND VESSEL; AND EXPLOSIVELY EXPANDING AT LEAST A PORTION OF SAID SECOND 